Process to produce void free refractory boride product



PROCESS TO PRODUCE VOID FREE REFRACTORY BQRIDE PRQDUCT Elwyn D. Fisher and Raymond EH. Baskey, Lakewood, Ohio, assignors to Horizons Incorporated, Cleveland, Ohio, a corporation N Drawing. Filed June 20, 1958, Ser. No. 743,501

2 Claims. (Cl. 75--202) This invention relates to a method of producing powder metallurgy compacts substantially porefree in nature. More particularly it relates to a method of incorporating an infiltrant into the voids in a powder metallurgy compact which contains as a principal constituent at least one material which is not readily wet by the infiltrant.

Prior efforts to produce materials for seals and bearings have focused attention on the carbides, silicides, borides and nitrides of the group IVA, VA and VIA metals and the prior art discloses the infiltration of compacts of such materials, as described for example, in Schwarzkopf Patent 2,422,439. We have found that the infiltration technique described in the patent does not yield entirely satisfactory results when applied to systems in which the infiltrant does not Wet one or more of the materials comprising the powder compact to be infiltrated and that to effectively produce an infiltrated article substantially devoid of pores, it is necessary to incorporate at least a fraction of the infiltrant into the preform prior to infiltration.

For purposes of illustration the present invention will be described in systems in which silver is the infiltrant and preforms of nickel and various borides comprise the matrix material which is to be infiltrated; it will be readily understood by others skilled in powder metallurgy that other refractory constituents may comprise the material infiltrated and that iron, cobalt and a host of ferrous and non-ferrous alloys could be present individually or in combination, in place of the nickel in the following ex amples and further that in place of metallic silver, silverbase alloys or other non-ferrous metallic materials could be employed, without departing from the scope of the present invention.

The following examples will serve to further illustrate the present invention and are to be taken as illustrative rather than limitative thereof.

Example 1 A powder metallurgy compact consisting of 27 parts by weight of tungsten boride and 3 parts of nickel was formed by intimately mixing plus 200 mesh, minus 325 mesh (Tyler standard) nickel and minus 325 mesh tungsten boride, and pressing the mixture in a die at about 25 tons per square inch. The resulting slug had an apparent density of approximately 80% of the theoretical density of such a mixture.

A solid silver slug weighing grams was placed in physical contact with the porous slug and the silver and compact were heated in a hydrogen atmosphere to about 1150 C. and maintained at that temperature for 120 minutes; during this heating, the silver melted and was drawn into the pores of the compact. When the infiltrated article was examined under a metallurgical microscope, it was observed that the silver had only partially penetrated the pores. Increasing the duration or temperature at which infiltration was effected did not materially decrease the extent of the unimpregnated area.

2,974,049 Patented Mar. 7, 1961 Example 2 The procedure of Example 1 was repeated except that between one third and one half of the silver was incorporated into the mixture of refractory boride and nickel prior to compacting and a lump of silver was placed in contact with the silver-containing slug. After heating, to melt the silver, as in Example 1, and to infiltrate the compact, it was found that the resulting material was completely free from any voids and that it possessed an excellent combination of properties as a rotating seal material, at elevated temperatures, e.g. 1000 to 1300" F., even in the absence of a lubricant.

Example 3 The procedures of Examples 1 and 2 were repeated with mixtures of the borides of the metals W, Mo, Cr, V, and Ti with and without the addition of some of the silver to the composition, prior to compacting, and in each instance it was found that the infiltrations performed as in Example 1 produced porous products, incompletely impregnated, whereas those processed in accordance with the procedure of Example 2 were free of gas pockets.

The following is a tabulation of some of the compositions processed as in the examples above. All infiltrations were for minutes at 1150 C. in hydrogen atmosphere.

Table I [No silver in mixture compacted] Powder Mixture Solid Product, Refractory Infiltrant, Density Refractory, Nickel, Ag Parts (percent of Parts Parts by wt. Theoretical) by Wt. by wt.

Chromium Boride.-- 27 s 10 45 Molybdenum Boride 27 3 10 40 Tungsten Boride 27 3 10 '34 Vanadium Boricle 21 9 10 6o Table II [Silver in compacted mixture] Powder Mixture, Solid Product, Parts by weight Infiltrant, Density Refractory Solid Ag (percent parts of Theo- Refrac N1 Ag by wt. rctical) tory Chromium Boride 18 6 6 10 97 Molybdenum Boride 21 3 6 10 96 Tungsten Boride 23. 7 1. 8 4. 5 10 99 Tungsten Boride 18 6 6 10 99. 5 Vanadium Boride 13. 5 6 10. 5 1O 94 While it is evident that substantial amounts of silver are infiltrated into the compositions in any event, it appears that to produce a void free product, it is necessary that at least 15-20% of the silver be included in the mixture prior to infiltration.

We claim:

l. A process for producing a pore-free product which comprises: forming an intimate mixture consisting essentially of nickel, silver and a refractory material which is not wet by silver and which is selected from the group consisting of borides of the metals W, Mo, Cr, V and Ti; compacting the mixture of refractory material and metals to form a compact having a density somewhat less than the theoretical density of said mixture; maintaining the compact in physical contact with additional silver and simultaneously therewith heating the additional silver and ture-.and.the remainder of the silver being atleast sufiicient to completely fill thevoids in said compact.

2.- The method of claim 1wherein the compactisgsintered andinfiltrated at about 1115'C. in'a hydrogen atmosphere.

References (Iited in the file of this patent UNITED STATES PATENTS Sieger -Dec. 11, 1934 Hensel et a1 Apr. 13, 1948 Goetzel Aug. 2, 1955 Hoyer Sept. 9, 1958 UNITED STATES PATENT OFFICE CERTIFICATIUN G CORRECTIQN Patent. No, 2,974,040 March 7, 1961 Elwyn Da Fisher et a1,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 1, for v1115 0." read 1150 C. --5

Signed and sealed this 1st day of August 1961.,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2,974,040 March 7, 1961 Elwyn D. Fisher et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 1, for 1115 0.". read 1150 c.

Signed and sealed this 1st day of August 1961.

( SEA L) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A PROCESS FOR PRODUCING A PORE-FREE PRODUCT WHICH COMPRISES: FORMING AN INTIMATE MIXTURE CONSISTING ESSENTIALLY OF NICKEL, SILVER AND A REFRACTORY MATERIAL WHICH IS NOT WET BY SILVER AND WHICH IS SELECTED FROM THE GROUP CONSISTING OF BORIDES OF THE METALS W, MO, CR, V AND TI, COMPACTING THE MIXTURE OF REFRACTORY MATERIAL AND METALS TO FORM A COMPACT HAVING A DENSITY SOMEWHAT LESS THAN THE THEORETICAL DENSITY OF SAID MIXTURE, MAINTAINING THE COMPACT IN PHYSICAL CONTACT WITH ADDITIONAL SILVER AND SIMULTANEOUSLY THEREWITH HEATING THE ADDITIONAL SILVER AND COMPACTED MATERIAL TO A TEMPERATURE AND FOR AN INTERVAL AT LEAST SUFFICIENT FOR THE ADDITIONAL SILVER TO MELT AND TO IMPREGNATE THE COMPACT TO SUBSTANTIALLY THEORETICAL DENSITY, THE RELATIVE AMOUNTS OF SILVER BEING SUCH THAT AT LEAST 15% OF THE TOTAL SILVER IS PRESENT IN THE ORIDGINAL MIXTURE AND THE REMAINDER OF THE SILVER BEING AT LEAST SUFFICIENT TO COMPLETELY FILL THE VOIDS IN SAID COMPACT. 